What is the ruling of the religion regarding the problem of obsessive-compulsive disorder, which manifests as constant thoughts of insulting the Divine Essence and thoughts of divorce despite not being married?

This type of waswas (whisperings) is dangerous and one of Satan's traps. Your friend should be guided to its peril and encouraged to remember Allah, recite the Quran, and occupy himself with what benefits him, because turning away from the remembrance of Allah, heedlessness, and idleness provide an opening for Satan. Allah the Almighty said: "And whoever turns away from the remembrance of the Most Merciful - We will appoint for him a devil, who will be to him a companion." (Quran 43:36). Neither prayer nor any other act of worship is lifted from him, and he is sinful for abandoning them.